1. Field of the Invention
The present invention pertains to combline filters and, in particular, to radio frequency band pass filters.
2. Description of the Related Art
Various filter designs have been proposed to allow certain frequencies to be transmitted to the output load while rejecting the remaining frequencies. Such filters designed for use in the frequency range of several hundred megahertz to one gigahertz include as an important example, combline strip line filters fixed to a design frequency. These types of filters are sometimes termed xe2x80x9cmechanicalxe2x80x9d filters, a reference to their physical construction. Combline filters of this type, especially when designed for high Q, low insertion loss applications, require demanding high tolerance O-ring and bushing components and correspondingly intricate assembly techniques, requiring substantial labor investment.
It is not uncommon, due to the long lead time sometimes required for fabrication and delivery, that the design frequency characteristics of an earlier fabricated filter may no longer precisely match requirements needed at the time of installation. In order to alter the center frequency of the filter, for example, the filter must be returned to the manufacturer for rebuilding. Time delays can be reduced by maintaining an inventory at the manufacturer""s site, although warehousing and storage costs incurred by the manufacturer are substantial and ultimately the purchaser incurs additional charges for the replacement service.